Diamond Grades 101: Diamond Grading FAQ

Loose Diamonds

In my last “101” post I gave you an overview of the world of diamond cutting. For Diamond Grades 101, I’ll be taking a different approach and answering some FAQs about how diamonds are graded, who grades them, and more.

Who grades diamonds? Where are they graded?

The Gemological Institute of America or the American Gem Society, also known as the GIA and AGS, grade the vast majority of diamonds. The GIA is by far the most popular grading lab. The GIA has 9 grading laboratories located all over the world. The GIA grading locations are: Carlsbad (California), New York City, Johannesburg (South Africa), Gaborone (Botswana), Ramat Gan (Israel), Bangkok, Mumbai, Tokyo, and Hong Kong.

Each diamond is graded multiple times by several different gemologists, who then compare their individual grades to reach a consensus. This careful, collaborative process is crucial to creating an accurate diamond grading report. Once a diamond has received its final official grade from the GIA, that grade usually stays with it for life. So, it’s important that the GIA gemologists are thorough when making grading decisions.


Sample GIA report with diamond grades
A sample GIA report. You can see a video of the diamond this report belongs to below.

How long does it take to grade a diamond?

Rush jobs can be completed in 2-4 weeks, but overall the turnaround time for grading a diamond is 60-90 days. Once the process is complete, the stone is then sent back to its owner with a GIA report or dossier that details the diamond’s grade.

Do diamond grades ever change?

If you send in a diamond to the GIA and you disagree with the grade your stone received, you can submit a formal protest and have the diamond re-graded. Most diamonds don’t require a second round of grading. For larger and higher quality stones, however, I’m sure you can picture how heated the debates can get between diamond suppliers and gemologists about the nuances of a stone’s grade.

What does my diamond’s grade mean? What determines a diamond’s grade?

A diamond’s grade is based on all of the 4 Cs – color, clarity, carat, and cut. Cut is the most recent addition to the diamond grading scale. It didn’t factor into a diamond’s grade until the late 2000s.

Ideal cut diamond
How an ideal cut promotes a diamond’s sparkle.

Because all 4 C’s are taken into account, a loose diamond’s final grade isn’t something as simple as “A+” or “8 out of 10”. Diamond grades include metrics for all 4 C’s. For example, the most common diamond grade is a G-F (color) VS2-VS1 (clarity) round (cut), falling between 0.5 – 0.75 carats. In the world of diamonds, all of these letters and numbers add up to mean, “the average”.

Can you tell a diamond’s grade based on its appearance?

Yes and no. This is where the relationship between diamond cutting and diamond grading gets tricky. Like I said in my Diamond Cutting 101 post, maximizing value and maximizing weight are the two most important things to consider before cutting a diamond.

Unfortunately, the value of a cut and its potential for getting a better grade from the GIA can often be at odds with each other. Certain cuts of diamonds will hide flaws better than others, but this doesn’t mean they are more valuable.

For example, take an emerald cut diamond compared to a princess cut. A flawless emerald cut is worth much more than a princess cut, because the facets on a princess cut diamond will hide its inclusions. Like so:

Princess cut diamond with VS1 clarity grade
A princess cut diamond with a VS1 clarity grade.

The flat plane of an emerald diamond will show inclusions whereas a princess diamond’s shape will hide them. Because it’s so easy to see the inclusions in an emerald cut diamond, an emerald cut with fewer inclusions is valued much higher than a similar princess cut. So, you can have emerald cut and princess cut diamonds that have the exact same grade, but totally different prices and appearances.

Emerald cut diamond with a VS1 clarity grade
Here’s an emerald cut diamond with the same clarity grade – VS1.  Much easier to notice the inclusion!

Now you have more insight on a diamond grade’s meaning, beyond just the numbers and letters. Feel free to share your diamond’s grade (with photos for reference!) and any more questions you have about diamond grading in the comments below.